1. Field of the Invention
The present invention relates to a semiconductor device manufacturing technology. More specifically, the present invention relates to a method for fabricating an Al-containing metal line in a semiconductor device.
2. Description of the Related Art
Conventionally, metallization interconnection technologies are applied in fabrication of semiconductor devices, in order to electrically interconnect circuit elements and/or other metallization lines. As a material for metallization interconnection, various metal materials such as aluminum (Al), tungsten (W), and copper (Cu) have been used, and especially Al has been most widely used among these metal materials.
In formation of Al contacts in semiconductor devices, a TiN layer has been used as a typical metal barrier. A metal barrier for Al contacts can comprise a TiN single layer or a Ti—TiN bilayer. A TiN barrier or Ti/TiN barrier can be generally formed on a bottom or sidewall of a contact, using a physical vapor deposition (PVD) process.
Hereinafter, a conventional method for fabricating an Al metallization line will be explained in detail, referring to the following drawings.
FIGS. 1A to 1C are cross-sectional views illustrating processes for fabricating Al metallization lines, according to a conventional art, and FIG. 2 is a SEM (Scanning Electron Microscope) image illustrating a problem in the conventional art.
Referring to FIG. 1A, an insulating layer 2 (i.e., a SiO2 layer) is formed on a semiconductor substrate 1 in which various circuit elements are previously formed, and then Ti and TiN layers 3 and 4 are formed in successive order on the insulating layer 2. After that, an Al layer 5 is formed on the TiN layer 4, and further another TiN layer 6 is formed on the Al layer 5. The TiN layer 6 functions as an anti-reflective coating to lower the reflection of light from the Al layer 5 during a photolithography process. In addition, the TiN layer 6 can be used as an etch stop layer during the process for forming a tungsten plug thereon.
As shown in FIG. 1B, a photoresist pattern 7 is formed on the TiN layer 6, using photolithography process, e.g., exposing and developing of a photoresist.
After that, as shown in FIG. 1C, the TiN layer 6, the Al layer 5, and Ti/TiN layer 3 and 4 are successively etched using the photoresist pattern 7 as an etching mask, thus forming Al metallization lines 10.
In the case of forming a single TiN layer (without a Ti layer) on the Al layer, as above described, a photoresist material can invade grain boundaries of the top TiN layer generally having a lamellar structure. Thus, a photoresist material can remain in the top TiN layer, even after the photolithography process. The remaining photoresist material may disturb patterning of the Al layer, thus resulting in a ring defect (referred to as A in FIG. 2) that represents non-etched Al material remaining between metal lines (referred to as ML in FIG. 2).
The ring defect A, abnormally interconnecting adjacent Al metal lines, may induce a failure of device operation.
For such reason, a Ti—TiN bilayer is generally used as a top metal barrier in formation of Al metal lines, wherein a top Ti layer can improve the adhesiveness and tolerance to electromigration (EM) of the Al layer. Especially, the top Ti layer can induce a crystal growth of Al in the direction of superior EM properties. Also, the top Ti layer can react with Al to form TiAl3, thus preventing crystal growth of Al in the form of a bamboo structure (or hillock).
In addition, because the top TiN layer has a lamellar structure but the top Ti layer may have little or no crystallinity, a photoresist material can not invade beyond the top TiN layer (i.e., up to the Al layer), thus the Al layer can be patterned normally.
However, forming the additional top Ti layer can cause another problem where the electric resistivity of the Al metal line increases. Accordingly, it may be desirable to remove the top Ti layer on the Al layer. Yet, in the case of removing the top Ti layer, a photoresist material for a photolithography process can contaminate Al metal lines, resulting in unwanted interconnection of neighboring metal lines.
In order to overcome such problems, especially the unwanted interconnection problem of metal lines, forming a SiO2 layer on the top TiN layer and then patterning the Al layer has been conventionally used.
Still, the patterning efficiency and gap-fill property of the Al layer may deteriorate due to the SiO2 layer. Particularly, voids may occur between metal lines. Accordingly, total processing margins may become insufficient, thus resulting in process control difficulties and productivity reduction.